6791
J . Org. Chem. 1995,60, 6791-6797
Synthetic Studies on Quinocarcin: Total Synthesis of (f)-Quinocarcinamidevia Dipole Cycloaddition of an Azomethine Ylide Generated by NJ3S Oxidation Mark E. Flanagan and Robert M. Williams* Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523 Received April 10, 1995@
The total synthesis of (f)-quinocarcinamide and a formal total synthesis of the antitumor, antibiotic quinocarcin involving a [3 21 dipolar cycloaddition reaction is described. The synthesis involves as a key step an NBS oxidation of an allylic tertiary amine to an imminium ion which is converted in situ into an azomethine ylide. Aspects of the ylide formation and a rationale for the regio- and stereocontrol for the cycloaddition process are discussed.
+
Introduction Quinocarcin (1)is natural secondary metabolite produced by Streptomyces melanovinaceusl and is the simplest member of the naphthyridinomycinhioxalomycid saframycin class of antitumor antibiotics. Quinocarcin displays weak antimicrobial activity against Gram-negative organisms and, as the citrate salt, displays promising antitumor activity against several lines of solid mammalian carcinomas including St-4 gastric carcinoma, co-3 human colon carcinoma, human mammary carcinoma, M5076 sarcoma, B16 melanoma, and P388 leukemia.2 The semisynthetic derivative of 1, DX-52-1 (2) also retains many of the antitumor properties exhibited by
1, Oulnocafcln,O W 2
2,
R z CN','DX-52-1
3. R = H. Qulnocarclnol
4, Qulnocarclnamlde
5 , Tetraromlne
1.3
Quinocarcin is coproduced with a biologically inactive reduction product, quinocarcinol(2), and we have shown4 that quinocarcin spontaneously disproportionates anaerobically into quinocarcinol and an oxidation product, quinocarcinamide(31, which is also biologically inactive. More recently, a new member of this class of compounds, tetrazomine (5), was isolated from Saccharothrk mutabilk, and preliminary antitumorhntimicrobial assays report activity similar to that displayed by quinocar~in.~Tetrazomine shows good antimicrobial activity against both Gram-negative and Gram-positive organisms and activity against P388 leukemia in vivo. The most complex members of this class of compounds includes the bioxalomycins (6-9) which have been isolated from Streptomyces sp. LL-31F508 that display potent antitumor activity as well as excellent activity against methicillin-resistant Staphylococcus aureus (MRSA).6 Bioxalomycin 8-2 was found to be identical to naphthyridinomycinproduced by Streptomyces lusitanus NRRL 8034; this work therefore established that the Abstract published in Advance ACS Abstracts, September 15,1995. (1)Tomita, F.; Takahashi, K.; Shimizu, K. J.Antibiot. 1983,36,463. (2) Fujimoto, K.; Oka, T.; Morimoto, M. Cancer Res. 1987,47,1516. (3) Saito, H.; Hirata, T.; Kasai, M.; Fujimoto, K.; Ashizawa, T.; Morimoto, M.; Sato, A. J. Med. Chem. 1991, 34, 1959. (4) Williams, R. M.; Glinka, T.; Flanagan, M. E.; Gallegos, R.; Coffman, H.; Pei, D. J.Am. Chem. Soc. 1992,114, 733. (51 (a) Sato, T.; Hirayama, F.; Saito, T. J.Antibiot. 1991,44, 1367. (b) Suzuki, K.; Sato, T.; Morioka, M.; Nagai, K.; Abe, K.; Yamaguchi, H.; Saito, T.; Ohmi, Y.; Susaki, K. J. Antibiot. 1991, 44, 479. (6) (a)Bernan, V. S.; Steinberg, D. A.; Montenegro, D. A.; Korshalla, J. D.; Maiese, W. M.; Greenstein, M. Abstracts of the 33rd ICAAC, New Orleans, LA, Oct 17-20, 1993; Abstract 570. (b) Steinberg, D. A.; Singh, M. P.; Jacobus, N. V.; Petersen, P. J.; Maiese, W. M.; Greenstein, M. Abstracts of the 33rd ICAAC, New Orleans, LA,Oct 17-20, 1993; Abstract 571. (c) Zaccardi, J.; Morton, G. 0.;Ascroft, J. S.; Tsao, R.; Siegel, M.; Maiese, W. M.; Ellestad, G. A. Abstracts of the 33rd ICAAC, @
8, R 7, R
= H Bloxa/omycln a-1 Me B/oxalmycln a-2
8, R
= ti Bloxakunycln &1
9, R
I
Me Bloxabmycln &2
hydrated form of naphthyridinomycin, is in fact, an artifact of the isolation procedure and that the primary biosynthetic product contains both oxazolidine rings intact. Modes of action for this class of compounds include the oxidative cleavage of DNA via the production of superoxide and the alkylation of DNA.4 Superoxide production by quinocarcin was first reported' by Tomita et al., and a mechanistic explanation has now been ~ f f e r e d . ~The ,~ ability to reduce molecular oxygen appears to be linked to the capacity for these compounds to undergo redox disproportionation reactions of their oxazolidine moieties which, under anaerobic conditions, lead to the products 3 and 4 (in the case of 1)and, under aerobic conditions, culminate in superoxide prod~ction.~ Preliminary mode of action studies in P388 leukemia cells demonstrated that quinocarcin blocks RNA synthesis in preference to DNA and protein synthesis, although a detailed mechanistic understanding of their cytotoxic properties has not been fully e l ~ c i d a t e d . ~ New Orleans, LA, Oct 17-20, 1993; Abstract 572. (d) Zaccardi, J.; Alluri, M.; Ashcroft, J.; Bernan, V.; Korshalla, J. D.; Morton, G. 0.; Siegel, M.; Tsao, R.; Williams, D. R.; Maiese, W.; Ellestad, G. A. J. Org. Chem. 1994,59,4045. (7) Tomita, F.; Takahashi, K.; Tamaoki, T. J. Antibiot. 1984, 37, 1268. (8)Williams, R. M.; Flanagan, M. E.; Tippie, T. N. Biochemistry 1994, 33, 4086.
0022-3263/95/1960-6791$09.00/00 1995 American Chemical Society
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J. Org. Chem., Vol.60,No.21, 1995
Due to the promising antibiotic and antitumor activities displayed by this class of compounds, interest in the total synthesis of the natural products and the synthesis of biologically active structural analogs has attracted considerable attention. Quinocarcinol methyl ester was synthesized by Danishefsky and co-workers in 1985.1° Fukuyama and Nunes reported the first total synthesis of (f)-quinocarcin,'l and more recently, two groups, Terashima and co-workers12 and Garner and co-worke r ~have , ~ achieved ~ syntheses of (-)-quinocarcin. We have been involved in the synthesis of biologically active structural analogs of quinocarcin which have focused on the construction of the biologically functional oxazolidine ring.14J5 Other noteworthy synthetic approaches to quinocarcin have also appeared in the literature,16 and a significant amount of activity on the total synthesis of the structurally related naphthyridinomycins (Le,,bioxalomycins)17and saframycinsl* has been reported. As part of our efforts to study the structural and stereoelectronic intricacies of the oxygen-dependent mechanism of DNA damage inflicted by this class of com(9)Jett, J. R.; Saijo, N.; Hong, W.-S.; Sasaki, Y.; Takahashi, H.; Nakano, H.; Nakagawa, K; Sakurai, M.; Suemasu, K.; Tesada, M. Invest. New Drugs 1987,5,155. (10)Danishefsky, S.J.; Harrison, P. J.; Webb, R. R.; ONeill, B. T. J. Am. Chem. SOC.1986,107, 1421. (11)Fukuyama, T.; Nunes, J. J. J . Am. Chem. Soc. 1988,110,5196. (12)(a) Saito, S.;Tamura, 0.; Kobayashi, Y.; Matsuda, F.; Katoh, T.; Terashima, S. Tetrahedron 1994,50,6193.(b) Saito, S.;Tanaka, K.; Nakatani, K.; Matsuda, F.; Katoh, T.; Terashima, S. Tetrahedron 1994,50, 6209. (c) Katoh, T.; Nagata, Y.; Kobayashi, Y.; Arai, K; Minami, J.; Terashima, S. Tetrahedron 1994,50,6221.(d) Katoh, T.; Kirihara, M.; Nagata, Y.; Kobayashi, Y.; Arai, K.; Minami, J.; Terashima, S. Tetrahedron 1994, 50, 6239. (e) Katoh, T.; Kirihara, M.; Yoshino, T.; Tamura, 0.; Ikeuchi, F.; Nakatani, K.; Matsuda, F.; Yamada, K.; Gomi, K.; Ashizawa, T.; Terashima, S. Tetrahedron 1994, 50,6259.(0 Katoh, T.; Kirihara, M.; Nagata, Y.; Kobayashi, Y.; Arai, K.; Minami, J.; Terashima, S. Tetrahedron Lett. 1993,34,5747. (g) Katoh, T.; Kirihara, M.; Nagata, Y.; Kobayashi, Y.; Arai, K.; Minami, J.; Terashima, S. Tetrahedron Lett. 1993,34, 5743. (h) Katoh, T.; Kirihara, M.; Nagata, Y.; Kobayashi, Y.; Arai, K.; Minami, J.;Terashima, S. Tetrahedron Lett. 1993,34, 5751. (i) Saito, S.;Tanaka, K.; Nakatani, K.; Matsuda, F.; Terashima, S. TetrahedronLett. 1989,30, 7423.(j) Saito, S.;Matsuda, F.; Terashima, S. TetrahedronLett. 1988, 29,6301. (13)(a) Garner, P.; Ho, W. B.; Shin, H. J . Am. Chem. SOC.1993, 115,10742.(b) Garner,.P.; Sunitha, K; Shanthilal, T. Tetrahedron Lett. 1988,29,3525.(c) Garner, P.;Sunitha, K.; Ho, W-B.; Youngs, W. J.; Kennedy, V. 0.;Djebli, A. J . Org. Chem. 1989,54,2041.(d) Garner, P.; Ho, W. B.; Grandhee, S. K.; Youngs, W. J.; Kennedy, V. O., J. Org. Chem. 1991,56,5893. (e) Garner, P.; Arya, F.; Ho, W. B. J. Org. Chem. 1990,55,412. (14)(a) Williams, R. M.; Glinka, T.; Gallegos, R.; Ehrlich, P. P.; Flanagan, M. E.; Coffman, H.; Park, G. Tetrahedron 1991,47,2629. (b) Williams, R. M.: Ehrlich, P. P.: Zhai,. W.;. Hendrix. J. J. O w- . Chem. 1987,52,2615. (15)Flanaean. M. E.: Rollins. S. B.: Williams. R. M. Chem. Biol. 1996,2, 147.- ' (16)For other synthetic approaches to quinocarcin, see: (a) Lessen, T. A.; Demko, D. M.; Weinreb, S. M. Tetrahedron Lett. 1990,31,2105. (b) Saito, H.; Hirata, T., TetrahedronLett. 1987,28,4065. For a related cycloaddition strategy, see: (c) Kiss, M.; Russell-Maynard, J.; Joule, J. A. Tetrahedron Lett. 1987,28,2187.(d) Allway, P.A.; Sutherland, J . K.; Joule, J . A. Tetrahedron Lett. 1990, 31, 4781. (17)For synthetic approaches and total syntheses of the naphthyridinomycins, see: (a) Fukuyama, T.; Li, L.; Laird, A. A.; Frank, R. K., J . Am. Chem. Soc. 1987,109,1587.(b) Fukuyama, T.; Frank, R. K.; Laird, A. A. Tetrahedron Lett. 1986,26, 2955.(c) Fukuyama, T.; Laird, A. A.Tetrahedron Lett. 1986,27,6173.(d) Evans, D. A.; Illig, C. R.; Saddler, J. C. J . Am. Chem. SOC.1986,108,2478.(e) Evans, D. A.; Biller, S. A. Tetrahedron Lett. 1985,26,1907.(f) Danishefsky, S.; ONeill, B. T.; Taniyama, E.; Vaughn, K., Tetrahedron Lett. 1984,26, 4199.( g ) Danishefsky, S.;O'Neill, B. T.; Springer, J. P. Tetrahedron Lett. 1984,25,4203. (18)For syntheses of the structurally related saframycins, see: (a) Fukuyama, T., Sachleben, R. A. J . Am. Chem. Soc. 1982,104,4957. (b) Fukuyama, T.; Linton, S. D.; Tun, M. M. Tetrahedron Lett. 1990, 31,5989.(c) Fukuyama, T.;Yang, L.; Ajeck, K. L.; Sachleben, R. A,, J . Am. Chem. SOC. 1990,112,3712.(d) Kubo, A.; Saito, N.; Yamato, H.; (e) Saito, Masubuchi, K.; Nakamura, M., J. Org. Chem. 1988,53,4295; N.; Yamauchi, R.; Nishioka, H.; Ida, S.; Kubo, A., J . Org. Chem. 1989, 54, 5391.
Flanagan and Williams U
U
12
10,Rr:Me 11, R = CH,COzH Y
W
14
pounds, we have reported the syntheses of the tetracyclic core analogs of quinocarcin 1O-14.l4J5 As an extension
Scheme 1
15
1
17
16
of this synthetic methodology, we now wish to report an efficient procedure for accessing the bicyclic pyrrolidinecontaining framework of these natural products which has resulted in the synthesis of (f)-quinocarcinamide (4). In addition, the route described herein intersects an intermediate in the total synthesis of (-)-quinocarcin reported by Garner and co-worker~.'~
Results Our initial approach to quinocarcin was directly analogous to that employed in the syntheses of 1O-14.l4J5Our strategy for generating the pyrrolidine ring (Scheme 1, 15) was to condense a sarcosine ester with the unsaturated aldehyde 16,generating the imminium ion in situ where upon treatment with base would lead to the intermediate azomethine ylide. Following ylide formation, [3 21 cycloaddition with an appropriate acrylate ester should afford a pyrrolidine displaying the regiochemical configuration illustrated by 15. This regiochemistry was anticipated based on the expectation that there would be preponderant negative charge density a to the sarcosyl ester moiety resulting in a larger HOMO coefficient at that center. If the proper relative stereochemistry in the pyrrolidine ring was obtained (particularly at C-8and C-ll)19 then conversion of this substrate
+
J. Org. Chem., Vol. 60,No.21, 1995 6793
Total Synthesis of (f)-Quinocarcinamide
Saponification of 17 with lithium hydroxide produced the corresponding /?-hydroxy acid. This material was carried on without purification by reaction with 3 equiv 1. LiOH, EtOH of thionyl chloride in refluxing toluene which resulted in /?-eliminationand acid chloride formation. The inter2. 2.3 eq. SOCIz mediate a,/?-unsaturatedacid chloride was then reduced toluene, A 3. NaBH4,CHzCh to allylic alcohol 18 with sodium borohydride in 42% 17 18 EtOH isolated yield from 17. 42% Swern oxidation of 18 afforded the a,/?-unsaturated aldehyde 16 in 98%yield. The cycloaddition reaction was then carried out by reacting 16 with 5 equiv of sarcosine DMSO MeHNACOzBn benzyl ester, 10 equiv of methyl acrylate, and 0.1 equiv =\ of triethylamine. ARer the mixture was refluxed in THF clcococl EtaN, CH&h THF,EbN COzMe OMe for 24 h, a 1:l mixture of pyrrolidine products (19) was 98% isolated in 62% yield. By lH N M R homo-decoupling and 16 62% NOE experiments;O both diastereomeric cycloadducts were determined to possess the regiochemistry and relative stereochemistry in the pyrrolidine rings illustrated in Scheme 2 which were epimeric about C-5. Consequently, only one of these compounds could possess the correct relative stereochemistry at C-11 (the nonepimerizable center) which meant that the incorrect stereochemistry was afforded at C-8 and C-10 for this to quinocarcin was to be accomplished by, first, reducing substrate. Efforts to control the cycloaddition reaction the double bond, second, selectively converting the sarby varying the ester substituents had only moderate cosy1 ester to the aldehyde oxidation state, and third, in effects on the ratio of products observed, and no new a manner analogous to that employed in the syntheses diastereomers were isolated. of 10-14, condense this aldehyde with the free amino In an effort to obtain the correct relative stereochemalcohol forming the labile oxazolidine in the last step. It istry in the pyrrolidine ring we modified our approach should be noted that related dipolar addition strategies to construct the by generating the dipole on a rigid, cyclic substrate. This were adopted by Garner13and Joule16C,d was accomplished by first preparing tricyclic monokepyrrolidine ring systems of quinocarcin. topiperizine 21 (Scheme 3). From allylic alcohol 18, Applying this strategy (Scheme 1)to the quinocarcin reaction with methanesulfonyl chloride followed by adsystem began with /?-hydroxy ethyl ester 17 (prepared dition of sarcosine ethyl ester afforded allylic amine 20 as a single diastereomer as previously described 14) which in 96% yield for the two steps. Saponification of the ethyl was subsequently converted to the a,/?-unsaturated alester and deprotection of the oxazolidinone afforded the dehyde 16 in four chemical steps (Scheme 2). Scheme 3
Scheme 2
vro
18
20
21 1. DMSO, CICOCOCI, Et3N
I
2. DBU, THF, rt 3. NaBH4,MeOH
-
22a, R = CHzOH 23a, R = CHO
MOMCI
22b, R CH20H 23b, R = CHO
FOzMe 1. Ra-Ni, EtOH b
Hz (1500 psi) 2. LiOH(q), EtOH 65% 24
&Me
(OMOM 0 25
4
6794 J. Org. Chem., Vol. 60, No. 21, 1995 intermediate amino alcohol. This material was then carried on without purification by cyclization with DCC and N-hydroxybenzotriazole(HOBT)producing amide 21 in 53% isolated yield for the two steps. A number of procedures were examined in an effort to oxidatively install a double bond in the C-ring, thereby generating the imminium precursor to the azomethine ylide. Attempts to generate the dipole via the N-oxide led to decomposition of the' substrate.21 Reaction of 21 with 1 equiv of NBS, in refluxing chloroform, however, did result in formation of the dark green imminium salt. Addition of triethylamine at 0 "C to this solution resulted in a dark blue solution which, upon warming to room temperature in the presence of methyl acrylate, resulted in the formation of a 5:l ratio of cycloadducts 22b and 22a,respectively (55%yield for the two steps). This ratio is presumably a manifestation of there being a preference for approach of the dipolarophile from the least hindered face. No other cycloadducts were isolated from the reaction mixture. Compounds 22a and 22b turned out to be diastereomeric about C-5, and both diastereomers possessed the correct regiochemistry and exo-configuration from the cycloaddition. Since the desired product (22a)was the minor diastereomer from the cycloaddition, 22b was subsequently efficiently epimerized to 22a in the following manner. Amido alcohol 22b was first subjected to Swern oxidation to give aldehyde 23b in 94% yield. Next, 23b was treated with 1 equiv of DBU in THF at room temperature for 3 h resulting in 80% conversion to aldehyde 23a. The NaBH4 reduction of 23a to 22a is a reaction that was first described in the total synthesis of quinocarcinol methyl ester by Danishefsky et al.,1° which completed the conversion of 22b to 22a in 78% overall yield based on 20% recovery of 23b. The alcohol moiety of compound 22a was then protected by reaction with chloromethyl methyl ether and Nfl-diisopropylethylamine affording 24 in 84% yield; this substance has been previously prepared by Garner and co-workers.13As previously described,1324 was converted to the acid 25 by Raney-Ni (Hz, 1500 psi) reduction of the double bond followed by saponification of the methyl ester with lithium hydroxide in 65% overall yield from 24. Finally, treatment of 25 with HC1 in water resulted in essentially quantitative conversion to (f)-quinocarcinamide(4)which was identical by lH NMR and mobility on TLC to an (19) The numbering of cycloadducts are based on the numbering for DX-52-1 (2) shown below.
(20) Results of NOE experiments for cycloadducts 14a and 14b. The additional diastereomeric center at C-5 is contained within "R".
M.
(21)Chastanet, J.; Roussi, G . J. Org. Chem. 1985, 50, 2910. Chastanet, J.; Roussi, G . Heterocycles 1985, 23, 653. Chastanet, J.; Fathallah, H.; Negron, G.; Roussi, G . Heterocycles 1992, 34, 1565.
Flanagan and Williams Scheme 4
'OH
Me0
20
:
22b
authentic sample of quinocarcinamide obtained by the autoredox disproportionation of quin~carcin.~ Compound 25 has been previously converted to quin~carcin'~ via partial reduction of the amide by dissolving lithium reduction and trapping the hemiaminal with cyanide to give DX-52-1(2).11J3 Quinocarcin (1)has been generated from DX-52-1 (2)under acidic or Lewis-acidic condition~.~*'~-'~
Discussion The use of NBS as an oxidant for the preparation of an azomethineylide is to our knowledge an unrecognized usage of this reagent. However, it is possible that the ability of NBS to carry out this transformation may be peculiar to this type of substrate. Preliminary attempts to carry out the analogous cycloaddition reaction on the corresponding C-lla(l2)-saturated substrate (DX-52-1 numberinglg) have, to date, been unsuccessful. The implication of this finding is the possible requirement for the carbon undergoing bromination to be allylic. Thus, bromination presumably occurs on the allylic carbon initially forming bromide 26 which immediately suffers elimination of the bromide producing 27. Aliquots of the reaction mixture after just 10 min revealed a new singlet in the lH NMR at 10.00 ppm indicative of the imminium methine. Also, the deep green color afforded is likely the result of extended conjugation upon formation of 27. The regiochemical outcome of the cycloaddition reaction is presumably a manifestation of structure 28 representing the major canonical form of the azomethine ylide. As in the previous cycloaddition reaction, this is the result of negative charge being effectively stabilized on the carbon a to the amide carbonyl. Due to the cyclic nature of 28,the cycloadducts formed are forced to have the correct relative stereochemical configuration between C-8 and (3-11. As compared to the cycloaddition reaction discussed above affording 19, which is most probably reacting through the "W" configuration of the ylide, such relative stereochemical control ambiguities do not exist for 28. The approach of the dipolarophile is presumably governed by the conformation of the ylide (structure 29, Scheme 4) which positions the hydroxymethyl group in a pseudoaxial orientation effectively shielding the bottom face of the ylide and favoring formation of the observed major isomer 22b.
Total Synthesis of (&I-Quinocarcinamide
The methodology described herein represents an efficient method to access the bicyclic &mework of quinocarcin which should be applicable to the other members of this class of antitumor antibiotics. This approach is particularly attractive because the starting isoquinoline 18 can be prepared efficiently on a large scale and all of the subsequent steps described are applicable to preparative scale chemistry. Although an epimerization is necessary in the final stages of the synthesis,this threestep procedure is efficient a n d benefits from a thermodynamically favored epimerization reaction. Additional applications of the chemistry described herein are currently being explored in these laboratories for synthetic access to tetrazomine, the bioxalomycins, and mechanism-based structural analogs that will be used in further exploiting t h e unique chemical reactivity of these oxazolidine-containing antitumor antibiotics. Experimental Section lH NMR and 13C NMR data was collected using a Bruker AC-300 (300 MHz) spectrometer, and NOE data was collected on a Bruker (500 MHz) instrument.
5-(Hydroxymethyl)10-methoxy3-oxo1,lob-dihydro5H-oxazolo-2,3-a]isoquinoline (18). To a stirred solution of 17 (prepared as described in ref 14) (11 g, 0.036 mol) dissolved in ethanol (360 mL) was added 2 M LiOH (36 mL, aqueous). The resulting mixture was stirred at 25 "C for 2 h at which time the reaction mixture was acidified to pH 5 with 1N HCl(aq), water (100 mL) was added and the mixture was extracted (3 x 200 mL) with dichloromethane. The dichloromethane layers were combined, dried over anhydrous Na2Sod, and concentrated to dryness in vacuo affording 9.4 g of the corresponding /3-hydroxy acid. This material was then slurried in dry toluene (375 mL), and to this mixture was added thionyl chloride (12.8 g, 0.108 mol). The resulting mixture was heated to reflux with stirring for 3 h. The reaction mixture was then cooled t o room temperature and concentrated under reduced pressure. Dichloromethane(250 mL) was added and the resulting solution cooled t o -78 "C. To this mixture was then added, over a 10 min period, an ice bath-cooled slurry of sodium borohydride (6.8 g, 0.18 mol) in ethanol (125 mL). The resulting mixture was warmed to room temperature, stirred for 2 h, and then cooled to 0 "C and carefully quenched with 1 N HCl(aq). The resulting mixture was then extracted with dichloromethane (2 x 200 mL), and the organic extracts were combined, dried over anhydrous Na2SO4,and concentratedto dryness in uacuo. The crude material was purified by flash chromatography(silica; 3:l ethyl acetate/ hexanes) affording 18 (oil, 3.7 g, 42% yield from 17). 'H NMR (300 MHz) (CDC13)6 TMS: 3.81 (3 H, s), 3.98 (lH, br s), 4.39 (1 H, dd, J = 6.6 , 13.6 Hz), 4.50-4.61 (1H, m), 4.54 (1 H, dd, J = 9.2, 11.5 Hz), 5.06 (1 H, dd, J = 7.9, 9.2 Hz), 5.28 (1H, dd, J = 7.9, 11.5 Hz), 5.93 (1H, s), 6.73 (1H, d, J = 7.1 Hz), 6.78 (1 H, d, J = 8.3 Hz), 7.23 (1H, t, J = 7.6 Hz). 13CNMR (74.47 MHz) (CDC13)6: 54.8 (d), 55.4 (91, 61.6 (t),70.6 (t), 110.0 (d), 111.7 (d), 117.5 (s), 118.4 (d), 129.1 (s), 129.5 (d), 132.0 (SI, 136.0(SI, 154.9(8). IR (NaCl): 3450,2938, 2841, 1756, 1645, 1602, 1576, 1477, 1446 cm-'. Anal. Calcd for C13H13N04: C, 63.15; H, 5.30; N, 5.67. Found: C, 63.40; H, 5.24; N, 5.60. 34[[(Ethoxycaronyl)aminolmethyll-l0-methoxy-3-oxo1,l0b-dihydro-5H-oxazolo[2,3-al-isoquinoline (20). To a stirred solution of 18 (400 mg, 1.62 mmol) dissolved in CH,Clz (14 mL) at 0 "C was added methanesulfonyl chloride (556 mg, 4.85 mmol) followed by triethylamine (820 mg, 8.10 "01). The resulting mixture was stirred at 0 "C for 30 min, and sarcosine ethyl ester hydrochloride (1.2 g, 8.10 mmol) (Aldrich) was added. The mixure was allowed to come to room temperature and stirred for 8 h. The reaction mixture was then concentrated under reduced pressure, redissolved in ethyl acetate (25 mL), passed through a short column of silica gel (eluted with ethyl acetate), and concentrated to dryness in Vacuo affording 20 (oil, 588 mg, 96%).
J. Org. Chem., Vol. 60, No. 21, 1995 6795 'H NMR (300 MHz) (CDC13) 6 TMS: 1.26 (3 H, t, J = 7.3 Hz), 2.53 (3 H, s), 3.43 (1H, 1/2 ABq, J = 16.9 Hz), 3.54 (lH, 1/2 ABq, J = 16.9 Hz), 3.59 (1H, 1/2 ABq, J = 14.9 Hz), 3.81 (3 H,s), 4.17 (2 H,q, J = 7.1 Hz), 4.33 (1H, l/ABq, J = 14.9 Hz), 4.49 (1H, dd, J = 9.2 Hz, J = 10.2 Hz), 4.98 (1H, dd, J =8.5Hz, J = 8 . 7 H z ) , 5 . 2 8 ( 1 H , d d , J=8.2Hz, J = 10.7Hz), 6.02 (1H, s), 6.74 (2 H, t, J = 8.4 Hz), 7.22 (1H, t, J = 7.8 Hz). 13CNMR(74.47 MHz) (CDC13) 6: 14.2 (91, 41.5 (q), 54.6 (d), 55.4 (q), 56.0 (t),57.4 (t),60.3 (t),69.4 (t),109.8 (d), 112.8 (d),118.2 (d), 119.0 (s), 129.3 (d), 132.3 (SI, 134.2 (s), 154.6 (SI, 154.9 (s), 171.0 (8). IR (NaCl): 2925, 2853, 1759, 1645, 1576, 1476 cm-l. Anal. Calcd for CleHnN2Os: C, 62.42; H, 6.40; N, 8.09. Found: C, 62.25; H, 6.60; N, 7.93.
2-Aza-6-(hydroxymethyl)-7-methoxy-2-methyl-4-oxo1,3,4,6,11,11a-tetrahydro-~-benzo[blquinolizine (21).To a stirred solution of 20 (252 mg, 0.666 mmol) in ethanol (33 mL) was added 2 M LiOH (aqueous, 3.3 mL). The reaction mixture was degassed by argon purge and the resulting mixture stirred at room temperature for 8 h. The solution was then cooled t o O°C, and the pH was adjusted to 5 with 6 N HCl(aq) and concentratedto dryness in uaeuo. The dry residue was then redissolved in DMF (10 mL) and cooled to 0 "C, and to this solution was added N-hydroxybenzatriazole (108 mg, 0.799 mmol) followed by DCC (165 mg, 0.700 mmol). The reaction was stirred at 0 "C for 1h and then allowed to come to room temperature and stir for an additional 18 h. After the reaction mixture was concentrated under reduced pressure at 35 "C, the residue was redissolved in CHzClz (50 mL), filtered through celite, washed with saturated NaHCOs(aq), dried over anhydrous NazS04, and concentratedunder reduced pressure. The crude material was then purified by flash chromatography (silica gel; 10:1 dichloromethane/methanol, 0.5% concd NH40H) affording pure 21 (oil, Rf = 0.53, 97 mg, 53% yield). 'H NMR (300 MHz) (CDC13) 6 TMS: 2.42 (3 H, s), 3.39 (1 H, 1/2 ABq, J = 13.6 Hz), 3.48 (2 H, SI, 3.55 (1H, 1/2 ABq, J = 13.6 Hz), 3.66-3.69 (2 H, m), 3.83 (3 H, s), 5.66 (1 H, s), 6.24 (1H, dd, J = 4.6 Hz, J = 7.0 Hz), 6.65 (1 H, d, J = 7.6 Hz), 6.74 (1H, d, J = 8.3 Hz), 7.18 (1H, t, J = 8.1 Hz) (note: the exchangeable proton was not observable). 13C NMR (300 MHz) (CDCl3) 6: 43.8 (q), 50.1 (d), 55.4 (91, 55.4 (t), 59.1 (t), 64.1 (t),106.3 (d), 109.3(d), 116.6(SI, 117.4(d), 128.9 (d), 131.6 (SI, 131.8 (4, 155.2(4, 166.6 (9). IR (NaCl): 3184,2939, 1680, 1643, 1474 cm-'; HRMS (FAB) calcd for C15H19N203 (MH+) 275.1396, found 275.1386. Methyl (50;~,10/?,1l/3)-5,7,8,9,10,1l-Hexahydro-4-methoxy-5-(hydroxymethyl)-13-methyl-7-oxo-8,ll-iminoazepino[1,2-b]isoquinoline-lO-carboxylate (22a)and Methyl (5a,8a,10~11a)-5,7,8,9,10,1l-Hexahydro-4-methoxy-5-(hy-
droxymethyl)-l3-methyl-7-0~0-8,1 l-iminoazepino[1,2-b]isoquinoline-10-carboxylate(22b). To a stirred solution of 21 (44 mg, 0.160 mmol) in CHC13 (11mL) was added NBS (28
mg, 0.160 mmol) and the resulting solution brought to reflux for 1 h (dark green color formed). At this time, the reaction mixture was cooled t o 0 "C, and t o the mixture was added methyl acrylate (687 mg, 8.00 mmol) followed by addition of a solution of triethylamine (162 mg, 1.60 mmol) in CHCl3 (5 mL) over a 15 min period (dark blue color formed). The reaction mixture was then allowed to come t o room temperature and stir for 1h. The reaction was then concentratedunder reduced pressure, redissolved in CH2C12, washed with saturated NaHCO3, dried over anhydrous NazS04, and concentrated t o dryness in vacuo. The crude material was then purified by PLC (silica gel; 3:l CHZClflHF, 0.25% concd NHdOH), affording 22a (oil, 5 mg, Rf = 0.38)and 22b (oil, 27 mg, R f = 0.24) (55%combined yield). 22a. lH NMR (300 MHz) (CDC13) 6 TMS: 1.79 (1H, br s), 2.46 (3 H, s), 2.54 (1H, dd, J = 9.81, 13.0 Hz), 2.61-2.69 (1 H,m),3.33(1H,dd,J=6.3,9.8Hz),3.59-3.65(1H,m),3.70 (1 H, d, J = 6.5 Hz), 3.76 (3 H, s), 3.84 (3 H, s), 4.04 (1 H, s), 5.70 (1H, s), 6.18 (1H, dd, J = 4.0, 8.1Hz), 6.68 (1H, d, J = 7.5Hz),6.75(1H,d,J = ~ . ~ H Z ) , ~ . ~ O ( ~ H , ~ , J = ~ . O H Z ) NMR (74.47 MHz) (CDC13) 6: 34.9,35.6,47.4,48.9, 52.4,55.4, 64.8, 65.3,66.9, 105.5, 109.4, 116.5, 117.7, 129.1, 131.2, 134.9, 155.2, 170.1, 173.6. IR (NaC1): 3425,2951, 2842, 1737, 1683,
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J. Org. Chem., Vol. 60,No. 21,1995
Flanagan and Williams
stirred at 0 "C for 1 h at which time the reaction mixture was 1642,1474cm-'. HRMS (FAB): calcd for C ~ S H Z ~(MH+): N~O~ allowed to warm t o room temperature with continued stirring 359.1607,found 359.1602 for an additional 16 h. The reaction mixture was then 22b. 'H NMR (300MHz) (CDC13)6 TMS: 2.10(1H, br s), 2.17(1H,dd,J=9.9,13.6Hz),2.62(3H,s),2.63-2.70(1H,concentrated under reduced pressure and purified by PTLC (silica gel; 3:lEtOAchexanes), affording 24 (oil, 6 mg, Rf = m), 2.88(1 H, dd, J = 4.8,10.0Hz), 3.67-3.76(1H, m), 3.76 0.30,84% yield). 'H NMR (300MHz) (CDC13) 6 TMS: 2.43(3H, s), 3.85(3H, s), 4.23(1 H, s), 5.67(1 H, s), 6.25(1 H, dd, 2.51(1H, m), 2.46(3H, s), 2.60-2.66(1H, m), 3.22(3H, s), J = 4.1, 7.3Hz), 6.67(1H, d , J = 7.6Hz), 6.75(1H, d , J = 7.6 Hz), 7.21(1H, t, J = 8.0 Hz). I3C NMR (74.47MHz) (CDC13) 3.28(1 H, dd, J = 9.9, 6.1Hz), 3.57-3.60(2H, m), 3.68(1 H, d, J = 6.4Hz), 3.77(3H, s), 3.84(3H, s), 4.03(1H, s), 4.44(1 6: 32.11,34.8,50.1,50.3,52.5,55.4,64.5,64.9,65.7,104.0, H,1/2ABq,J=6.5Hz),4.64(1H,1/2ABq,J=6.5Hz),5.70 109.2,115.9,117.2,129.1,132.3,136.5,155.3,171.4,173.3. IR (NaCl): 2950,1734,1684,1636,1474 cm-l. Additional (1H, s), 6.22(1H, dd, J = 4.6,6.6Hz), 6.66(1H, d, J = 7.6 structural characterization was provided for this compound Hz), 6.73(1 H, d, J = 8.3Hz), 7.18(1 H, t, J = 8.0 Hz). I3C by the conversion into 22a,described below. NMR (300MHz) (CDCl3) 6: 34.6, 35.7,46.0,47.4, 52.5,55.2, Methyl (5o;8o;10a,lla)-5,7,8,9,lO,ll-Hexahydro4-meth- 55.4,65.5,66.9,67.1,96.1,105.7,109.2,117.2,117.5,128.8, oxy-5-formyl13-methyl-7-oxo-8,1l-iminoazepino[ 1,241 IR (NaCl): 2949,1738, 1686, 131.5,134.9,155.2, 168.8,173.7. isoquinoline-10-carboxylate (23b). To a solution of DMSO (MH+) 1546,1474cm-l. HRMS (FAB): calcd for CZIHZ,NZO~ (31mg, 0.402mmol) in CHzClz (2.5mL) and cooled t o -78 "C 403.1869,found 403.1872. was added oxalyl chloride (26mg, 0.201"01) and the mixture Methyl (So;8/3,10/3,11/3,11~)-5,7,9,10,11,1 la,l2-Octahystirred at -78 "C for 10 min. A solution of 22b (36mg, 0.100 dro-4-methoxy-5-[(methyoxymethoxy)methyl]-l3-methmmol) in CHzClz (1.0mL) was then added and the resulting y1-7-0~0-8,1l-iminoazepino[ 1,2-b]isoquinoline-l0-carboxsolution stirred at -78 "C for 1 h, at which time triethylamine ylate. This procedure has been described previously by (101mg, 1.00mmol) was added and the reaction mixture was Garner et al.I3 A high pressure hydrogenation bomb was allowed to warm t o room temperature. The reaction was then charged with compound 24 (21mg, 0.052mmol) dissolved in concentrated under reduced pressure, redissolved in CHzClz absolute EtOH (4mL) followed by a slurry of washed W 2 (20mL), washed with water, dried over anhydrous NazS04, Raney-Ni (200pL, Aldrich). The mixture was then subjected and concentrated to dryness in vacuo affording 23b (oil, 34 to high pressure hydrogenolysis (Hz, 1500psi) for 20 h at 65 mg, 94% yield). lH NMR (300MHz) (CDCl3) 6 TMS: 2.22(1 "C. After cooling, the reaction mixture was then filtered H, dd, J = 9.8, 13.5Hz), 2.62-2.71(1H, m), 2.79(3 H, s), through Celite and concentrated under reduced pressure. The 2.93(1 H, dd, J = 5.0, 9.8Hz), 3.74-3.80(1 H, m), 3.76(3H, crude mixture was then separated by PTLC (silica gel; 3:l s), 3.90(3H,s),4.21(1H, s), 5.59(1H, s), 6.58(1 H, s), 6.68(1 EtOAchexanes), affording the pure methyl ester of compound H, d, J = 8.3Hz), 6.80(1 H, d, J = 7.8Hz), 7.25(1 H, t, J = 25 l3 (oil, 10 mg, Rf = 0.22,45% yield). 8.0 Hz), 9.35(1H, s). 13C NMR (300MHz) (CDCl3) 6: 32.7, 'H NMR (300MHz) (CDC13) 6 TMS: 2.29(1H, dd, J = 9.6, 35.0,49.8,52.5,55.6,58.1,64.9,65.3,102.8,109.1,110.8,117.9, 13.1Hz), 2.49(3 H, s), 2.53(1 H, dd, J = 2.3,14.2Hz), 2.57130.1,132.1,137.4,155.5,169.6,173.2,191.3. IR (NaC1): 2.65(1 H, m), 2.96(3H, s), 3.14(1 H, t, J = 13.5Hz), 3.36(1 2948,2852,1735,1686,1645,1475 cm-'. HRMS (FAB): calcd H, dd, J = 6.8,9.6Hz), 3.53-3.57(2H, m), 3.65(1 H, d, J = for C19HzlNzOs (MH+)357.1450, found 357.1451. 2.6Hz), 3.76(3H, s), 3.82(3H, s), 4.23(1 H, dd, J = 3.0, 9.9 EpimerizationofAmido Aldehyde 23b to 23a. Methyl Hz), 4.29(1H, 1/2ABq, J = 6.3Hz), 4.42(1H, 1/2ABq, J = (5a,8/3,10/3,11/3)-5,7,8,9,10,1 l-Hexahydro-4-methoxy-S- 6.3Hz), 5.61(1H, t, J = 2.4Hz), 6.77(2H, t, J = 9.1Hz), formyl-13-methyl-7-oxo-8,1l-iminoazepino[ 1,2-b]isoquin7.18(1 H, t, J = 7.9Hz). 13C NMR (74.47MHz) (CDC13) 6: oline-10-carboxylate, 23a. To a stirred solution of 23b (30 32.1,34.4,37.0,41.3,49.4,52.4,54.3,54.7,55.3,66.4,67.1, mg, 0.084mmol) in dry THF (10mL) was added DBU (13mg, 68.0,96.3,108.7,119.5,122.6,127.8,138.2,155.7, 171.0,174.9. 0.084 mmol) and the resulting mixture stirred at room IR (NaCl): 2949,1735,1655,1474,1265 cm-'. HRMS (FAB): temperature for 3h. The reaction was then dilluted with CHzcalcd for CzlHz~NzO6(MHf) 405.2026, found 405.2027. Clz (25 mL), washed with saturated NaHCOdaq), dried over (5a,~,lqS,1~,1laS)-5,7,9,10,11,11a,l2-Odahydro-4-methanhydrous NazS04, and concentrated to dryness in uacuo. The oxy-5-[(methyoxymethoxy)methyll-13-methyl-7-oxo-8,11crude product was then purified by PTLC (silica gel; 3:lEtOAd iminoazepino[l,2-b]isoquinoline-l0-carboxylic Acid (25). 23a (oil, 22 mg, Rf = 0.41) and 23b (oil, 6 hexanes) affording To a stirred solution of the methyl ester obtained above (10 mg, Rf = 0.50). mg, 0.025mmol) dissolved in EtOH (0.5 mL) was added LiOH 23a. 'H NMR (300MHz) (CDC13) 6 TMS: 2.50(3 H, s), (0.8 mg,0.037 mmol) in water (20pL). The resulting mixture 2.64-2.71(2H, m), 3.54(1 H, dd, J = 6.4, 9.5Hz), 3.73(1H, was stirred at room temperature for 1.5h at which time the d, J = 6.4Hz), 3.76(3H, s), 3.92(3H,s), 4.07(1H, s), 5.61(1 H , ~ ) , 6 . 5 7 ( 1 H , s ) , 6 . 7 0 ( 1 H , d , J = 7 . 5 H z ) , 6 . 8 2 ( 1 H , d , J = solution was diluted with water (5 mL), acidified to pH 5 with 1 N HCl(aq) and the mixture extracted 3 x 10 mL with 8.3Hz), 7.27(1 H, t, J = 8.7Hz),9.29(1 H, s). I3C NMR (74.47 dichloromethane. The extracts were combined, dried over MHz) (CDC13)6: 34.9,35.6,47.8,52.5,55.6,56.5,65.2,66.5, anhydrous NazS04, and concentrated to dryness in vacuo, 104.1,109.3,111.2,118.2,130.1,136.0,155.5,168.5,173.8, affording 10 mg of crude product. An aliquot was purified by 192.1.IR (NaC1): 2951,2842,1734,1687,1647,1475 cm-'. PTLC (silica; 8:l chlorofodmethanol) producing a pure HRMS (FAB):calcd for C19H21Nz05 (MH+) 357.1450,found sample of 25 (oil, Rf = 0.30). 'H NMR (300MHz) (CDC13) 6 357.1465. TMS: 2.28(1H,t,J=9.8Hz),2.45-2.53(2H,m),2.54(3H, Reduction of 23a to Amido Alcohol 22a. To a stirred ~),2.92(3H,s),3.11-3.20(1H,m),3.25(1H,dd,J=4.8,9.6 solution of 22a (14mg, 0.039mmol) in anhydrous MeOH (3 Hz), 3.49-3.57(2 H, m), 3.60(1 H, br s), 3.81(3H,s), 3.84(1 mL) and cooled to 0 "C was added NaBH4 (6mg, 0.157 mmol) H, d, J = 9.0Hz), 4.17(1H, dd, J = 2.8,10.0Hz), 4.26(1 H, (Baker) and the resulting mixture stirred at 0 "C for 1 h. The 1/2ABq, J = 6.3Hz), 4.36(1H, 1/2ABq, J = 6.3Hz), 5.60(1 reaction mixture was then carfully quenched by addition of 1 H, br s), 6.67(1 H, d, J = 7.5Hz), 6.75(1 H, d, J = 8.3Hz), N HCl(aq) until bubbling subsided. This solution was then 7.13(1 H, t, J = 7.9Hz) (note: the exchangeable proton was concentrated under reduced pressure and the residue redisnot observable). 13CNMR (74.47MHz) (CDC13)6: 35.2,49.4, solved in CHzClz (10mL), washed with saturated NaHCOa(aq), 54.8,55.3,67.8, 96.3,108.8,119.5, 122.5,128.1, 138.2,155.7, dried over anhydrous NazS04, and concentrated to dryness zn 176.3.IR (NaC1): 3448,2944,1652,1591,1474,1460,1265 uacuo, affording 22a (13mg, 94% yield). Physical data for 22a cm-l. HRMS (FAB): calcd for C Z O H Z ~ N(MH'): Z O ~ 391.1869, reported above. Methyl (5a,8/.?,10/3,11/3)-5,7,8,9,10,1l-Hexahydro-4-meth- found 391.1877. oxy-5-[(methoxymethoxy)methyl]-13-methyl-7-oxo-8,11- (A)-Quinocarcinamide(4). Compound 25 (6 mg) was dissolved in HzO (1.0mL) and treated with 3 drops of 1 N iminoazepino[1,2-b]isoquinoline-1O-carboxylate (24).To HC1 at room temperature for 8 h. The mixture was concena stirred solution of 22a (6mg, 0.017mmol) dissolved in CHZtrated under reduced pressure to give 5.5 mg (quant) of the Clz (2mL) and cooled to 0 "C was added of Nfl-diisopropylHCl salt (amorphous powder). Dissolution of this substance ethylamine (7 mg, 0.051 mmol) followed by chloromethyl in DzO with the addition of ca. 1 mg of sodium carbonate methyl ether (3 mg, 0.043mmol). The resulting mixture was
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J. Org. Chem., Vol. 60, No. 21, 1995 6797
Total Synthesis of (f)-Quinocarcinamide revealed by lH NMR analysis that compound 25 was quantitatively converted into (*)-quinocarcinamide (4). The synthetic material matched an authentic sample prepared by the autoredox disproportionation of natural quinocarcin as previously described by 'H NMR and TLC behavior.
Acknowledgment. This research was supported by "he National Institutes of Health (Grant No. CA43969). We would also like to thank the Central Instrument Facility, Colorado State University, for mass spectral analysis of compounds and for conducting NOE experiments. We would also like to thank Professor Samuel
Danishefsky for providing an
N M R spectrum of syn-
thetic quinocarcinamide methyl ester. Supporting InformationAvailable: lH NMR spectra of all new compounds and comparison spectra of synthetic and natural quinocarcinamide;experimental preparation for compounds 16,19 and sarcosine benzyl ester are also included (14pages). This material is contained in libraries on microfiche, immediatelyfollows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information. 509506847
